Fluoropolymers are known to be useful as processing aids when used in low concentration in other polymers to mitigate effects such as melt fracture or high torque that limit rate of extrusion of these host polymers, thereby improving processibility. Polyolefins are a class of host polymers of particular interest.
Blatz in U.S. Pat. No. 3,125,547 discloses the use of fluoropolymers in polyolefins to facilitate extrusion. A general requirement taught by Blatz is that the fluoropolymer must be molten or fluid at the processing temperature T.sub.p of the polyolefin. Various two-component process aids have been identified in attempts to achieve better performance than that provided by the single component or Blatz. For example, Chapman & Priester in U.S. Pat. No. 4,904,735 disclose a synergistic combination of solid and fluid fluoropolymers, e.g., a fluoroelastomer and an unmelted fluoroplastic, to achieve enhanced process aid performance. As a further example, Duchesne & Johnson in U.S. Pat. No. 4,855,360 disclose a combination of a fluorocarbon polymer and a poly(oxyalkylene) polymer to reduce melt defects in extruded hydrocarbon polymer. Also, Priester & Stewart in co-pending U.S. patent application Ser. No. 08/196,740 (1994) disclose polar-side-group-containing extrusion adjuvants that counteract the deleterious effect of certain additives on the effectiveness of fluoropolymer processing aids in polyolefins.
In terms of achieving greater effect at lower concentration of costly fluoropolymer, further improvement in the efficiency of fluoropolymer processing aid systems is desired.